To cite package ‘optim.functions’ in publications use:

Torsney-Weir T (2017). optim.functions: Standard Benchmark Optimization Functions. R package version 0.1, https://CRAN.R-project.org/package=optim.functions.

Corresponding BibTeX entry:

  @Manual{,
    title = {optim.functions: Standard Benchmark Optimization
      Functions},
    author = {Thomas Torsney-Weir},
    year = {2017},
    note = {R package version 0.1},
    url = {https://CRAN.R-project.org/package=optim.functions},
  }